KR20000060200A - Manufacturing method of silica glass for sol-gel process - Google Patents

Abstract

PURPOSE: A manufacturing method for silica glass for sol-gel process is provided to remove the air that remains in the silica glass, so that the density and the transparency can be improved. CONSTITUTION: A manufacturing method for silica glass comprises the steps of; making sol by mixing silica, dispersing agent, gelling agent, deionized water and binding agent; removing the seed of sol and molding and then gelling; demolding and drying the gel; removing an organic matter from the dried gel by treating with heat at temperatures of 300-600°C and then removing the hydroxyl group; removing the residual gas in vacuum state, and repeating the process of pumping an inert gas; treating with heat in helium gas at temperatures of 1100-1400°C, so that the purity of silica glass is improved.

Description

Manufacturing method of silica glass for sol-gel process

The present invention relates to a method for producing silica glass for sol-gel process, and more particularly, to a method for preparing silica glass for sol-gel process, which improves density and transparency characteristics by removing air remaining in silica glass. .

The sol-gel process is a liquid phase process, which has high productivity and can freely control the composition of the product, and because the process is generally performed at a low temperature, it is very economical and is very useful when manufacturing high purity silica glass for optical fibers or semiconductors.

Hereinafter, a brief description of a method of manufacturing a silica glass overcladding tube using a sol-gel process is as follows.

First, silica particles are dispersed in water to form a sol. The sol formed is left to mature for a predetermined time. The aged sol is then poured into a mold and gelated. Once gelling is complete, the gel is separated from the mold and then dried.

Thereafter, the dried gel is first heat treated to remove organic matter in the gel. Subsequently, the gel from which the organic matter is removed is left to stand for a predetermined time in an air atmosphere and room temperature, and then vitrified by removing the hydroxyl group.

Thereafter, the resultant product is subjected to a sintering reaction to complete a silica glass overcladding tube.

As described above, after removing the organic substances in the sol, it is common to undergo a process of leaving the mixture in an air atmosphere and room temperature before vitrification. However, due to such a process, some of the fine bubbles remain in the finally obtained silica glass tube, causing cloudiness, thereby degrading the transparency characteristics of the silica glass tube, thereby deteriorating the molding density characteristics.

The technical problem to be achieved by the present invention is to solve the above problems to provide a method for producing a silica glass for sol-gel process with improved transparency and molding density characteristics of the silica glass.

In the present invention to achieve the above technical problem. (a) mixing silica, dispersant, binder, gelling agent and deionized water to form a sol;

(b) removing the bubbles from the formed sol and then molding and gelling;

(c) demolding the obtained gel to dry it;

(d) removing organics from the dried gel and then removing hydroxyl groups;

(e) repeating the process of removing residual gas and adding an inert gas under vacuum conditions several times; And

(F) provides a method for producing a silica glass for sol-gel process comprising the step of sintering the result.

Argon, nitrogen or helium gas is used as the inert gas in step (d).

Preferably, the organic material removal process of step (d) is performed by heat treatment at 300 to 600 ℃. And the step of removing the hydroxyl group of the step (d) is made by heat treatment at 500 to 1000 ℃ in a chlorine gas atmosphere, and the sintering process of (f) is preferably made by heat treatment at 1100 to 1400 ℃ under a helium gas atmosphere. .

The production method according to the present invention is intended to suppress the adverse effects of air remaining in the vitrification process and subsequent processes after the removal of organic matter and hydroxyl groups in the gel and before the vitrification step of the gel. It is a feature to provide a method of efficiently removing air prior to vitrification. In the present invention, as a method for efficiently removing air, a method of repeatedly removing a residual gas and a process of adding an inert gas by using a vacuum pump is used, and thus the atmosphere in the process tube for vitrification. Into the inert atmosphere it is possible to obtain a dense silica glass tube.

The method for producing silica glass according to the present invention having the above-described characteristics will be described in more detail.

First, silica, additives and deionized water are mixed and then a sol is formed. Subsequently, bubbles are removed from the sol using a vacuum pump.

Although the said additive is not specifically limited, A dispersing agent, a binder, a plasticizer, a gelling agent, etc. are used. Herein, the dispersant, binder, plasticizer, and gelling agent are not particularly limited as long as they are materials commonly used in the production of silica glass. And the content of each substance is also normal.

The gelling agent is a water-soluble aliphatic ester of an acid selected from the group consisting of formic acid, lactic acid and glycolic acid, and specific examples thereof include methyl formate, methyl lactate, ethyl lactate, and the like. As the dispersant, tetramethylammonium hydroxide and tetraethylammonium hydroxide which are quaternary ammonium hydroxides are used. These materials not only help the silica to be uniformly dispersed in the composition, but also serve to electrostatically stabilize the sol in which the silica is dispersed.

In addition, a polyhydric alcohol (polyhydric alcohol) is used as a plasticizer. Specific examples include glycerin, ethylene glycol, 2-methylpropane-1,2,3-triol, and the like. As the binder, polyethyloxazoline, polyvinylacetate, or the like is used.

The sol formed according to the above procedure is molded and then gelled. Subsequently, when the gelation is completed after a predetermined period of time, the gelled resultant is de-molded.

The demolded gel is then dried at a temperature of 30-80 ° C. and a relative humidity of 65-80%.

The dried gel is then heat treated at 300 to 600 ° C. to remove the organics remaining in the gel. Subsequently, in order to vitrify the gel, the gel is heated at 500 to 1000 ° C. for a predetermined time. This heat treatment is carried out in a chlorine gas atmosphere in which residual hydroxyl groups are removed.

Then, the resultant is allowed to stand at room temperature and in air for a predetermined time.

Thereafter, the gas existing in the process tube is removed using a vacuum pump, and then an inert gas is added thereto. This degassing process and inert gas charging process are repeated several times, preferably two to three times, to form an atmosphere in the process tube as an inert gas atmosphere.

The resultant is then heated to 1100 to 1400 ° C. (heating rate: 100 ° C./hr) in a helium gas atmosphere and heat treated for about 5 hours to complete the silica glass tube.

The silica glass manufacturing method described above is a method that can be usefully applied regardless of the specifications of the silica glass overcladding tube.

Example 1

500 g of fume silica (Aerosil OX-50, Degussa), 52 ml of 25 wt% tetraammonium hydroxide (TMAH) aqueous solution, 500 g deionized water, 60 g ethyl lactate and 2.1 g polyethyloxazoline are mixed To form a sol.

The sol was then aged for 15 hours and then bubbled from the sol using a vacuum pump. This bubble-free sol was poured into a mold and gelated.

Once gelling was complete, the wet gel was removed from the mold and dried for 4 days at 30 ° C. and 80 RH% in a thermo-hygrostat.

Subsequently, the dried gel is heated up to about 500 ° C. (raising rate: 50 ° C./hr) and heat-treated at this temperature for 5 hours to remove organic matter contained in the gel, and then, at about 1000 ° C. under a chlorine (Cl ₂ ) gas atmosphere. Heating rate: 100 ° C./hr) for 5 hours to remove residual hydroxyl groups in the gel. Subsequently, residual chlorine gas was removed at about 500 ° C. using oxygen (O ₂ ) gas and helium gas. Then, it was left for 24 hours at room temperature in the air.

Then, the residual gas was removed using a vacuum pump, and then helium gas was added. This process was repeated 2-3 times.

The resultant was sintered at about 1400 ° C. (heating rate: 100 ° C./hr) for 4 hours under a helium atmosphere to complete a silica glass tube. At this time, the inner diameter of the silica glass tube was 22 mm, the outer diameter was 67 mm, and the length was 1000 mm.

Example 2

A silica glass tube was prepared in the same manner as in Example 1 and Example 1, except that argon gas was used instead of helium gas.

Example 3

Silica glass tubes were prepared in the same manner as in Example 1 and Example 1, except that nitrogen gas was used instead of helium gas.

Comparative example

Silica glass tubes were prepared in the same manner as in Example 1, except that residual gas was removed using a vacuum pump, and then a process of adding helium gas was omitted.

Molding density and transparency of the silica glass tubes prepared according to Examples 1-3 and Comparative Examples were measured.

As a result of the measurement, the silica glass tube manufactured according to Example 1-3 had a higher compaction density as a densified state than in the comparative example. In addition, the silica glass tube prepared according to the comparative example appears to be generally cloudy when visually observed due to fine bubbles, whereas the silica glass tube prepared according to Examples 1-3 does not appear to exhibit such a phenomenon, thereby improving transparency characteristics. I could confirm that.

According to the present invention, it is possible to obtain silica glass having improved densification characteristics while improving mold density characteristics by densifying by removing air remaining in the gel.

Claims (5)

(a) mixing silica, dispersant, binder, gelling agent and deionized water to form a sol; (b) removing the bubbles from the formed sol and then molding and gelling; (c) demolding the obtained gel to dry it; (d) removing organics from the dried gel and then removing hydroxyl groups; (e) repeating the process of removing residual gas and adding an inert gas under vacuum conditions several times; And (f) a method for producing silica glass for sol-gel process comprising the step of sintering the resultant. The method of claim 1, wherein the inert gas is helium, nitrogen, or argon gas. The method of claim 1, wherein the step of removing the organic matter of step (d) is made by heat treatment at 300 to 600 ℃ sol-gel manufacturing method for silica glass. The method of claim 1, wherein the hydroxyl group removing step (d) is performed by heat treatment at 500 to 1000 ° C. under a chlorine gas atmosphere. The method of claim 1, wherein the sintering process of the step (f) is made by heat treatment at 1100 to 1400 ℃ under a helium gas atmosphere.